Abstract: More cuttings produced during gas drilling due to higher mechanical penetration rate and the cuttings usually tend to be larger in the bottom and smaller uniform in size when back to the wellhead. It is indicating that cuttings should appear successive breaking within the process of migration. According to particle collision broken theories, the successive breaking phenomenon was analyzed, and the calculating method of crash velocity for the occurrence of secondary breaking was given in this paper. Meanwhile, the breaking process matrix and the particle size distribution function were applied to study the re-cracking process of cuttings migration in the whole wellbore. The calculating results show that the cuttings in the wellbore were broken first in the form of the uneven size volumetric fracturing and then progressively turned into the surface fracture of the uniform process, and ultimately was tending towards stable particle size distribution state.